(1) Field of the Invention
The invention relates to a turbo-machine device for automatically controlling the rate of flow of turbine ventilation air.
Research on improved performance in modern turbo-machines has resulted in an increase in operating temperatures, in turn requiring new materials satisfying these conditions of use. The control of thermal expansion and the need for improved operational behaviour and increased length of life of components has also led to a need for complex cooling systems which, in particular, use air bled from the cold parts of the machine to ventilate hotter parts, such as the turbine for example. Technical development has in fact been accompanied by a substantial increase in the temperatures at the turbine inlet.
One factor which also influences performance, and particularly efficiency or maximum thrust in aeronautical applications, is the control of minimal but adequate clearance between stationary and rotating parts of the turbo-machine. One of the means conventionally used to match the radial expansion or contraction of a stator element at a radial end of a rotating part (a rotor blade or element) to the radial movements of said end is to provide ventilation for the stator element.
It will therefore be apparent that control of the rates of flow of ventilation air is an important factor in controlling the operating conditions of a turbo-machine, irrespective of the use of such air, two examples of which are indicated above in connection with the cooling of the turbine elements or adjusting the operational clearances between the rotor and stator.
(2) Summary of the Prior Art
U.S. Pat. No. 3,975,901, for example, describes a device which meters a mixture of two gas flows at different temperatures, the mixture being applied to a turbine stator wall by means of a shutter which moves radially with respect to two gas passages, the movement being produced by thermal expansion. However, the use of such a device is a sensitive and complex matter and requires the use of two gas sources at different temperatures.
U.S. Pat. No. 3,029,064 describes means for controlling the supply of air to cooling chambers disposed around a turbine casing comprising butterfly valves, the movement of which is controlled by the differential expansion of a ring divided into cylindrical segments, each associated with a valve and having one end secured to the casing and the other connected to the valve. This device uses a plurality of valves, the lack of reliability of which may jeopardise its efficiency.